1. Field of the Invention
The invention relates to control of a printing apparatus for receiving print information from a plurality of computers on a network via a predetermined interface and processing it.
2. Related Background Art
In recent years, an information processing system in which a color printing apparatus and a plurality of host computers can communicate with each other has been generalized and widely used. In such a situation, many electronic documents are formed on the information processing system, there is a tendency such that an output request to the color printing apparatus is increasing, and a high-speed color printing apparatus of a low cost is demanded.
Hitherto, in a print system for interpreting a page description language (PDL) transmitted from a host computer or a print server and forming a raster image, generally, the PDL is interpreted, thereafter, a display list (DL) as an intermediate language is formed, and raster image conversion (rendering) from the DL is executed.
At this time, since a size of the PDL data is not limited, there is a case where a size of DL which is formed from the PDL data is very large. If the DL is complicated and its size increases, a work area which is used by a renderer for rendering the DL also increases.
However, since an amount of memory which is provided in the printing apparatus is limited and there is a limitation of costs, in many cases, there is not an enough amount to store the DL.
Therefore, a size of area to store the DL and a size of work area which can be used by the renderer are limited and there is a limitation such that a DL of a predetermined size or more cannot be processed.
A process called a fallback is executed to avoid such a limitation. According to the fallback, when the size of DL exceeds the predetermined size or if it is known that the size of work area for processing the DL exceeds the predetermined size, the DL formed once so far is rendered so as to form a raster image and the DL formed so far is cleared once.
The raster image is added again as a background image of a drawing area to a part of the DL.
Ordinarily, since the background image is compressed, a size of DL which is added is smaller than the original DL size. Therefore, by forming the residual DL into the empty area, the DL of a large size can be processed in the limited memory space. Since the work area of the renderer is also cleared when the rendering at the time of the fallback is finished, the size limitation of the work area can be also avoided and the printing apparatus of a low cost can be provided.
Although the raster image formed in the step of executing the fallback process as mentioned above is compressed and added to a DL list, the compression image which is formed at this time has to be also enclosed in the predetermined size.
Particularly, since the size of raster image which is formed upon rendering in the case of a color image is very large and, in many cases, the compression image cannot be enclosed in the predetermined size in the case of reversible compression, irreversible compression is ordinarily used.
However, if the irreversible compression is used, a compressed image deteriorates. As a method of minimizing such image deterioration, while sequentially changing a compression ratio from a low compression ratio to a high compression ratio (from the compression of small image deterioration to the compression of large image deterioration), the rendered image is compressed a plurality of number of times until the compression image is enclosed into the predetermined size. By using such a method, the image is compressed at the minimum compression ratio at which it is enclosed into the predetermined size and the image deterioration is minimized. For example, refer to JP-A-H7-137355 (U.S. Pat. No. 5,835,122).
However, the compression ratio of the raster image depends on the contents of the raster image and there is a case where the compression ratio fairly deteriorates even in the compression in which image deterioration of a similar degree occurs.
In the case of such a raster image, the compression which causes large image deterioration has to be executed in order to enclose the image into the predetermined size. Picture quality of the compression image deteriorates fairly. In many cases, there is a problem such that a print output including such a deteriorated compression image is different from a desired output of the user.